Cataract is the clouding of the eye's natural lens and commonly results in blindness. In Singapore alone, cataract affects more than 80% of people aged 60 and above. As life expectancy continues to increase, it is expected that every individual will at some point of his life undergo cataract surgery. Today, cataract surgery is in fact the most common surgery across all fields of medicine with an estimated 20,000,000 surgeries performed each year worldwide. Cataract surgery involves removing the ‘cloudy’ lens and replacing it with an optically clear implant, referred to as an intraocular lens (IOL) implant.
To ensure the success of cataract surgery, there is a strong clinical need for a clear and unobstructed view of the lens for the surgeon. The lens is covered in part by the iris—the muscle tissue that is responsible for opening the pupil. In other words, for cataract surgery to succeed, the ophthalmic surgeon requires an adequately large pupil opening.
Several clinical options are already available to enlarge the pupil during cataract surgery. The most common approach is pharmacological, and involves using dilating eye drops. Eye drops, however, are controlled substances, which can cause side effects such as allergic reactions and conjunctival injection. Eye drops have been found to be ineffective, either through a partial or total lack of dilation, in a substantial number of patients.
An alternative approach to enlarge pupils is mechanical, and relies on temporarily inserting a mechanical device (iris/pupil expander) into the front chamber of the eye (anterior chamber) to apply a mechanical force to the iris, thus enlarging the pupil.
Iris (or pupil) expanders have been available since the 1980s. Earlier iterations were made from flexible resilient materials like silicone, directly inserted into the eye via a corneal incision. The ring pushes against one portion of the pupil and is then slotted in to the remainder of the iris to create mechanical circular dilation of the pupil. The Iris Retractor (U.S. Pat. No. 4,387,706), developed by Robert M. Glass, was one such example. However, an issue with using such pupil expanders is that large corneal incisions are required which may lead to prolonged post-operative recovery.
To temporarily stretch the pupil, the surgeon can use instruments such as a Sinskey hook, or a Beehler pupil dilator. For these hooks, they are introduced through two incisions in the cornea and engage the iris at opposite ends. The hooks are then pulled apart in opposite directions to cause micro tears in the iris sphincter that result in a slightly enlarged pupil size. But the use of these hooks can be counter-productive if done incorrectly and may cause iris prolapse out of the incision by rendering it too floppy.
There are other drawbacks to mechanical stretching and sphincter cuts. Firstly, the micro tears caused to the iris sphincter muscle are irreversible. Although, usually asymptomatic, in some cases they could lead to postoperative bleeding, pigment dispersion, atonic pupil shape and minimal dilation. For Sinskey hooks, the mean pupil size achieved is 4.9±0.7 mm while for Beehler pupil dilators, the mean pupil size achieved is 5.5±0.8 mm. The relatively small dilation size achieved may not justify the possible permanent damage to the iris.
One of the oldest and most popular iris expanders are iris hooks. Four iris hooks evenly spaced 90° apart from each other resulting in a diamond shaped opening. This method is relatively simple to execute, but adds on a mean time of 297±51 seconds for insertion to the surgery (Akman et al, 2004) and sometimes lifts the pupil edge up, making surgery more challenging. Having four additional incisions also increases the chances of infection and post-operative inflammatory response. Even so, the maximum pupil dilation achieved was reported to be only a 5.5 mm diameter circle. Iris hooks can also damage the pupillary margin, which results in prolonged abnormal dilation. The unique advantage is their flexibility in being able to also hook into the capsular bag, if needed, to stabilize this in cases of zonulysis and the crystalline lens is tipping downwards.
Recent designs of pupil expanders have favored slimmer and flexible rings e.g. the Malyugin Ring, whose four corner helical loops engage the iris. Similarly the Oasis Ring, substitutes pockets for loops. However, the ring can flip out of plane and damage the cornea. The iris margin can also become temporarily caught by the helical loops and some force is required to pull out the ring, and it can be traumatic to the iris margin to insert through a small pupil and may interfere with surgery becoming dislodged during the phacoemulsification. Further, the downside of such rings is that insertion through a very small 3 mm pupil is impossible and such ring can only be used to expand a moderately dilated pupil to a larger one. The Bhattacharjee Ring is an alternative that has six points of capture, but is fiddly to insert and remove. The Assia pupil expander is a new, metallic, crude square pupil expander that is not widely used but requires additional moderate size incisions.
The Perfect Pupil is a flexible polyurethane iris expansion ring. It has a luxurious internal diameter of 7 mm. The Perfect Pupil is first inserted fully into the anterior chamber of the eye so that it is resting on the iris. The surgeon then engages the primary fenestration before proceeding around. It will typically take an average of 4 minutes for insertion and withdrawal. In addition, the attachment of the fenestrations can cause iris chafing to occur. The Perfect Pupil is also not fully circular in configuration, but rather is a configured into a 270°-320° circle sector.
Older pupil expansion rings include the Morcher 5S Pupil and the disposable silicone Eagle Vision Graether Ring both of which are threaded along the pupillary margin using an injector. However, these rings are difficult to position if the anterior chamber is shallow or the pupil is less than 4 mm wide.
As can be seen, most of these pupil expanders are crude and poorly designed. Most of these pupil expanders are also difficult to insert, deploy and retract into a truly small diameter pupil and if so, do not manage to dilate the pupil very dramatically. Furthermore, some of these pupil expanders require corneal incisions for insertion. Some of these pupil expanders deform the pupil to a square-shaped opening, which is unnatural. In addition, some of these pupil expanders can result in considerable damage and trauma to the iris, thus highly impacting its functionality. As such, they cannot be considered as true substitutes for pupil dilation with drops prior to surgery or prior to Femtosecond Laser-Assisted Cataract Surgery (FLACS).
Accordingly, example embodiments seek to provide an expander for widening and holding apart an opening in a tissue and a method of operating the expander that addresses at least some of the issues identified above.